The present invention relates to a high-voltage transformer having a core, a primary winding, a high-voltage winding being arranged in a coil former and a housing. Transformers of this kind are especially applicable in television sets and computer monitors.
A widely used type of this high-voltage transformer is explained by means of FIGS. 1a to 1c: In FIG. 1a a first coil former 11 of the high-voltage transformer is shown having a cylindrical part which holds a primary winding W1 and a bottom part with terminals 10 which provide connections to a printed circuit board. Through an opening 9 of the coil former 11 a ferrite core K is fit, usually a U/U-core.
In FIG. 1b a coil former 13 is shown with chambers 4 in which the high-voltage winding WH is arranged. The high-voltage winding WH is separated by diodes D into partial windings to work as a diode-split high-voltage transformer. The number of diodes D depends on the required high-voltage value and the beam current for a certain picture tube, they can be placed above the high-voltage winding WH on walls separating the chambers 4 as well as separately in additional chambers. The high-voltage coil former 13 fits tightly over the cylindrical part with the coil former 11 of the primary winding W1.
Coil former 13 and coil former 11 are covered by a housing 12 shown in FIG. 1c. It is open at the bottom side facing the printed circuit board and comprises two holes 14 and 15 through which the ferrite core K is fit. It comprises further in this embodiment two chimney-like terminals 5 and 6 for the high-voltage cable and the focus cable.
In the international patent application WO 99/03118 a diode split high-voltage transformer is disclosed in which the primary winding is placed on top of the high-voltage winding, the high-voltage windings therefore lying between the primary winding and the core. At the end of the production the housing 12 is placed over the coil former of the high-voltage winding WH and the coil former 11 with the primary winding W1 and filled up with resin to avoid high-voltage sparking and corona effects inside of the high-voltage transformer.
This object is achieved by means of the invention as specified in claim 1. Advantageous developments of the invention are disclosed in the subclaims.
In the case of the high-voltage transformer of the invention the primary winding is not arranged inside of the housing but outside directly on the housing. Providing the housing with a cylindrical shape it is for example only necessary to arrange two wall-like extensions or juts at the housing between which the primary winding can be wound. The winding can be done automatically in the production as known before and can be arranged as a dense package.
In an advantageous embodiment the primary winding extends in its width completely over the chambers of the high-voltage winding to provide a good electrical shielding for the high-voltage transformer. Also, auxiliary windings for additional voltages which are usually provided by the high-voltage transformer can be placed outside of the housing above the primary winding. The housing can furthermore hold up the diodes being placed above the high-voltage winding and the terminals for the focus and the high-voltage cable as done by the former types.
The transformer comprises only two plastic parts which requires less production steps and less material. Because primary and auxiliary windings are placed outside the housing the volume of the housing is much reduced and therefore much less resin is required to fill up the high-voltage transformer. This leads to a considerable weight reduction. The voltage isolation of the primary and the auxiliary windings is no problem for the safety and the reliability of the high-voltage transformer because isolated wires are used. Only the high-voltage winding has to be isolated with resin.